Some borrowers can’t keep up with their mortgage payments because they’re struggling to make ends meet.

Others choose not to keep up even though they can afford their monthly payments, and a new picture is emerging about who these borrowers are and why they walk away.

A growing body of research shows that these so-called “strategic defaulters” defy the tell-tale characteristics of most people whose loans go bad. They pay their bills on time, rarely exceed their credit-card limits and hardly use retail credit cards, according to a study released Thursday.

And they plan ahead.

They know their credit scores will take a hit after they fall behind on their mortgages, so they tend to open new credit cards in advance of defaulting, according to Thursday’s study, conducted by FICO, the firm that created the nation’s most widely used credit scoring system.

“These are savvy people who organize themselves,” said Andrew Jennings, FICO’s chief analytics officer. “This is a planned activity, not an impulse activity.”

This relatively new type of behavior is the latest sign of just how profoundly the mortgage crisis has reshaped consumer attitudes toward their homes and their finances. It is largely driven by plunging home values, which have left nearly a quarter of the nation’s homeowners underwater, or owing more on their mortgages than their homes are worth.

So some do the math and walk.

A team of researchers estimated that 35 percent of defaults in September may have been strategic, up from 26 percent in March 2009. But they acknowledge in a report published last month that the numbers are tough to tease out because “strategic defaulters have all the incentive to disguise themselves as people who cannot afford to pay,” according to the report by researchers from the European University Institute, Northwestern University and the University of Chicago.

That’s because lenders have become more aggressive about trying to recoup money lost on foreclosures, and they’re chasing after borrowers who they suspect have skipped out on a loan they could have paid.

In many localities — including Virginia, Maryland and the District — lenders have the right to pursue those borrowers and collect the difference between what the property sold for in foreclosure and what the borrower owed on it, also called a deficiency.

A handful of states do not allow lenders to pursue deficiencies. But in states that do, the laws vary widely. Some states limit how long the banks have to file a claim or collect the debt. Others may calculate deficiencies based on the fair-market value of the house. For instance, if a home sells for $200,000 yet its fair market value is $250,000, the borrower who owes $240,000 on the mortgage would not have a deficiency.

Many borrowers may not be aware of these laws. Instead, their decision on whether to strategically default may be tied more to emotion than anything else, the team of university researchers concluded in last month’s study.

They found that people are less willing to strategically default if they think it’s immoral. They are more likely to do it if they are angry about their financial situation or mistrust the banks and want them to be better regulated. They are also more willing to proceed if they know someone who defaulted strategically.

A year ago, another report added to the body of data being gathered about these borrowers. Those who have high credit scores and new mortgages with relatively large balances are more likely to default than those who don’t, Morgan Stanley analyst Vishwanath Tirupattur wrote.

Morgan Stanley’s analysis is cited in the FICO study and meshes with FICO’s conclusions. FICO defined strategic defaulters as borrowers who are underwater on their loans and fell 90 days behind on their mortgage yet kept up with all their other debts — a departure from the traditional pattern of a typical struggling borrower.

But Sam Khater, a senior economist at the mortgage research firm CoreLogic, said it’s important to put the numbers in perspective when trying to figure out how big a challenge these borrowers pose for the lending industry and the housing market at large.

The more people who default, for any reason, the tougher it will be for the housing market to recover. Foreclosures sell at a steep discount and drag down the value of the properties around them. Clearing them off the market is key to a rebound.

But even though 11 million homeowners in this country are underwater, only 7 percent of them have defaulted, Khater said. If every one of those loans belonged to a strategic defaulter, an unlikely scenario, it’s still a relatively small number, Khater said.

Still, “strategic default starts to make sense for borrowers who are extremely underwater on their loans with little prospect for price recovery,” Khater said. “But the factors pushing underwater borrowers toward strategic default are beginning to fade in part because home prices are nearing the bottom.”

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